1. Field of the Invention
The present invention relates to a cooling control unit and a method therefore for an electrophotographic apparatus, which fixed toner onto a sheet of paper during printing by controlling temperature to a printing temperature, and upon stoppage, cools an increase in temperature caused by a fixing unit and the like. More particularly, the invention relates to a cooling control unit and a method therefor for an electrophotographic apparatus, which controls a cooling fan by predicting an increase in temperature from the control status of the fixing unit without the need for a temperature sensor.
2. Description of the Related Arts
In a conventional electrophotographic apparatus such as a laser printer, provided with an apparatus cooling fan, toner is fixed on a sheet of paper by temperature-controlling a heater of a fixing unit. The fixing unit is controlled to a printing temperature of, for example, 150.degree. C. during printing, and to a standby temperature of, for example, 120.degree. C. during stoppage of printing. A cooling fan is therefore provided for the purpose of inhibiting an increase in machine internal temperature of the electrophotographic apparatus. The cooling fan is forcedly cooled through circulation of air under rotational control during printing. In a printing standby state of waiting printing, however, various motors for printing control are not driven, the cooling fan left to be driven only shows up wind howls. The wind howls may be prevented by discontinuing driving of the fan during stoppage of printing. Immediately after end of printing operation, however, the heat from heat generating components such as the heater of the fixing unit during printing causes an increase in the machine internal temperature. As a result, when fan driving is discontinued with stoppage of printing, there occurs an overshoot in which the machine internal temperature in creases over a safety temperature range, and the increase in temperature may cause occurrence of toner blocking or breakage of electric parts. In order to avoid this inconvenience, it is necessary to keep driving the fan for a certain period of time after stoppage of printing, or continue fan driving until the machine internal temperature is reduced to a safe level by providing a machine internal temperature sensor.
However, in a configuration in which the fan is driven for a certain period of time after stoppage of printing, it is necessary to drive the fan for the certain period of time even when the period of printing operation is short and the machine internal temperature is not so high, and during this certain period, occurrence of noise caused by extra fan driving poses a problem. In a configuration in which fan driving is continued until the machine internal temperature decreases to a safe level by providing an internal temperature sensor, the timing to stop the fan can be accurately known, but it is necessary to install the temperature sensor in the apparatus, thus leading to problem of a complicated apparatus configuration and a higher cost.